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Supporting Multiple Pointing Devices in Microsoft Windows

Michael Westergaard

Department of Computer Science

University of Aarhus

Denmark

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Outline

• Why multiple pointing devices?

• Requirements

• Architecture– Framework

– High-level API

– Low-level API

– Device driver

– Example

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Why Multiple Pointing Devices

• Demonstration

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Why Multiple Pointing Devices (2)

• Advanced interaction techniques– Multiple hand interactions

• Two-handed resize/zoom

• Two handed rotation of 3D objects

• Three handed zoom + move + rotate

– Different mice for different tasks

– Floating palettes

– Tool glasses

• Move work from one hand to another reduce risk of cumulative trauma disorders

• Cooperative work (for example on a wall PC)

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Requirements

• Earlier: External application directly polling hardware. This requires exclusive access to the (serial) port

• Support arbitrarily many mice

• Treat USB, serial, and PS/2 mice alike

• Wish to use mouse in “old” Windows applications

• Generic solution not tied to a specific application or framework

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Architecture

Hardware dependent driver

Device driver

Low-level API

High-level API

Framework

Windows mouse

subsystem

Framework

Application Low-level API

Main topic of article

Octopus

CPN Tools

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ArchitectureFramework

Hardware dependent driver

Device driver

Low-level API

High-level API

Framework

Windows mouse

subsystem

Framework

Application Low-level API

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Framework

• Provide widget-like interface (for example one can override the OnMouseDown event of a Button )

• Must also provide information about what mouse was clicked (this can be obtained by adding a Mouse property to the MouseEventArgs along with information about all mice on the system )

• Must also provide information about other mice working with an element (just another property of MouseEventArgs ) in order to allow exclusive access to an element and to allow multiple hand actions

• Give mouse back to Windows when it leaves application window (only when no native support is available, of course)

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ArchitectureDevice Driver

Hardware dependent driver

Device driver

Low-level API

High-level API

Framework

Windows mouse

subsystem

Framework

Application Low-level API

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Device Driver

• Windows does not distinguish between different mice

• Install filter between hardware dependent driver and Windows Mouse subsystem– We do not have to deal with hardware differences

– We can select whether to send a mouse event to Windows

• Keep driver as simple as possible to avoid bugs in kernel-mode code– Use callback to send data to user-mode

– Communicate by creating files in the drivers namespace

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Device Driver (2)

• Interface

• A finite state machine is implemented

Name Description

Get Hook up a mouse for use by an application, register a callback, stop sending Windows mouse events

UnGet Release a mouse, drop the callback and start sending Windows events again

Suspend Temporarily suspend a mouse, keep the callback but start sending Windows events

UnSuspend Stop sending Windows events

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Device Driver (3)

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ArchitectureLow-level API

Hardware dependent driver

Device driver

Low-level API

High-level API

Framework

Windows mouse

subsystem

Framework

Application Low-level API

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Low-level API

• Hide operating system specific support (for multiple mice) from higher levels– Simple C interface rather than operating system specific calls

to communicate with device driver

– If generic Windows support is developed only the low-level API needs to be changed

• Simplify identification of mice

• Add simple error handling

• Calls are not thread-safe

• Designed to be statically linked to a specific application

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Low-level API (2)• Interface

• The provided callback does not have to be thread-safe

Name Description

RegisterCallback Register a callback

GetMice Hook up a specified number of mice

HasMouse Query if we have hooked a mouse with a specified number

UnGetMouse Release a specified mouse

SuspendMouse Passed to the device driver

UnSuspendMouse Passed to the device driver

UnRegisterCallback Drop a previously registered callback

UnGetAllMice Release all hooked mice

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ArchitectureHigh-level API

Hardware dependent driver

Device driver

Low-level API

High-level API

Framework

Windows mouse

subsystem

Framework

Application Low-level API

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High-level API• Hide the underlying operating system from the

framework• Build on top of low-level API• Spawn a thread to listen for callbacks from the low-

level API• Send “mouse events” to application• Calls are thread-safe• Draw mouse cursors• Accelerate mouse• Offer polling interface• Like low-level API designed to be statically linked to

an application

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High-level API (2)• Interface

Name Description

Initialise Start up the listener thread and do some other initialising

Cleanup Kill the listener thread and cleanup other allocated resources

SuspendMouse Thread-safe version of corresponding low-level functionsUnsuspendMouse

GetRelativePosition Get mouse movement since last call

GetAbsolutePosition Get the position of the mouse

SetAbsolutePosition Set the position of the mouse

SetCursor Set the cursor for a specified mouse

LockCanvas Used for drawing cursors

UpdateCursors Used for drawing cursors

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ArchitectureExample -- Startup

Application Framework H-API L-API Driver User

StartStart

Initialise

GetMice

Get

Getn times

n

spawn

n

ok

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ArchitectureExample -- Suspend

Application Framework H-API L-API Driver User

Move mouseMouse movedcallbackMouse moved

callbackMouse movedevent

Mouse ismoved outof window Suspend

Suspend

Suspend

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Future Work

• More control of what mice are hooked by GetMice function (by number, name, position on bus, or capabilities)

• Be able to handle multiple applications sharing mice

• Higher-level API: DLL/System service

• Port the needed layers to also support Windows 9x/ME/NT, Unix, and Mac

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Conclusions

During this talk we have…

• seen how multiple mice can be useful (advanced interaction techniques, cooperative work)

• seen requirements for an architecture supporting multiple mice (work with any kind of mouse, backwards compatibility, not tied to an application)

• seen requirements for a framework supporting multiple mice

• seen a device driver and two supporting APIs that can satisfy the needs of a framework supporting multiple mice

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FrameworkWidgets With Events

public class MyButton: Button { protected override void OnMouseDown(MouseEventArgs e) { base.OnMouseDown(e);

if (e.Button == left) { MessageBox.Show("Button pressed", ""); } }}

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FrameworkKnowledge of Active Mouse

public class MyButton: Button { protected override void OnMouseDown(MyMouseEventArgs e) { base.OnMouseDown(e);

if (e.Mouse == Mice[1]) { MessageBox.Show("Mouse 1 pressed", ""); } }}

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FrameworkKnowledge of Other Mice

public class MyButton: Button { protected override void OnMouseDown(MyMouseEventArgs e) { base.OnMouseDown(e);

if (e.OtherMice.Length == 0) { MessageBox.Show(“Only one mouse pressed the button", ""); } }}